An electrical switch is often associated with the master cylinder of motor vehicle hydraulic brake systems for the purpose of, for example, energizing a stop light circuit and/or deenergizing a cruise control circuit upon application of the brakes by the driver. Such electrical switches are generally of the pressure operated type. That is, they are operated by the increase of hydraulic fluid pressure when the brake pedal is displaced such as to cause a corresponding displacement of the master cylinder piston, thus increasing the pressure of the hydraulic fluid in the master cylinder in front of the piston. Pressure operated switches are costly to manufacture and they must be installed, at least partly, within the master cylinder. They are also often unreliable as they must be activated by a slight increase in the hydraulic fluid pressure for providing an appropriate stop signal even upon slight application of the brakes or for disconnecting the cruise control system as the result of a slight foot tap on the brake pedal. Further, the functioning of pressure operated switches may be somewhat erratic under certain conditions, such as in the presence of hydraulic fluid back pressure surges in the master cylinder caused, for example, by heat expansion of the brake linings and of the hydraulic fluid. Such erratic functioning of pressure operated switches causes erratic turning on and off of the motor vehicle stop signal lights, particularly irritating to the driver of a motor vehicle immediately following.
Hydraulic control apparatus for motor vehicle mechanical clutches are readily becoming the standard of the industry for operating the clutch release mechanism of a motor vehicle provided with a mechanical clutch and the conventionally manually shiftable transmission or gearbox. Examples of such hydraulic control systems for mechanical clutches are disclosed in U.S. Pat. Nos. 4,407,125, 4585,108, 4,585,109, 4,585,106, 4,585,107, and 4,599,860, and in U.S. Pat. Nos. 4,684,003 and 4,624,290 and in co-pending application Ser. No. 555,666, all assigned to the same assignee as the present application.
It has become general practice in the automobile industry to interlock the operation of the engine starter motor with other controls of the motor vehicle such that the starter motor is rendered inoperative unless the transmission is in neutral or park in motor vehicles provided with an automatic transmission or, in motor vehicles provided with a foot operated clutch and a manually operated gearshift transmission, unless the transmission is in neutral and/or the clutch pedal is fully depressed to fully release the clutch. In addition, it is convenient, in motor vehicles provided with a cruise control and a mechanical clutch, to shut off the operation of the cruise control upon, for example, downshifting which in turn requires release of the clutch. However, it is desirable that the cruise control be disconnected even before the clutch is fully released to enable the driver to cut off the cruise control by a slight foot tap on the clutch pedal, and perhaps to discourage "riding" on the clutch, that is, resting one's foot on the clutch pedal at all times.
In prior applications Ser. Nos. 080,196 and 878,121, there are disclosed mechanically operated limit switches, mounted on the input member of a hydraulic control system, such as a clutch hydraulic control or a brake hydraulic control, which are directly operated by the master cylinder input member. Whereas these mechanically operated switches avoid the recited problems with the prior art pressure operated switches and are generally satisfactory, they tend to complicate the assembly process of the associated hydraulic control system by virtue of their disposition on the input member of the master cylinder.